Semiconductor devices are built up using a number of material layers. Each layer is patterned to add or remove selected portions to form circuit features that will eventually make up an integrated circuit. Some layers can be grown from another layer; for example, an insulating layer of silicon dioxide can be grown over a layer of silicon by oxidizing the silicon surface. Other layers are formed using deposition techniques, typical ones being chemical vapor deposition (CVD), evaporation, and sputtering.
Deposition methods form layers using vaporized materials that condense to form a film on the surface of interest. Unfortunately, the films thus formed are not limited to the surface of interest, but tend also to form on other surfaces within the reaction chamber. Thus, after substantial use, a thick film of the deposited material accumulates on components and surfaces within the reaction chamber. As the film grows inside the chamber, the film becomes an increasingly troublesome source of contaminants. Etch processes also contaminate inside surfaces of reaction chambers, though by different mechanisms. In either case, the reaction chamber, including internal components, must be periodically cleaned or replaced.
FIG. 1 (Prior Art) depicts a cross-section of a typical cleaning system, or xe2x80x9cbench,xe2x80x9d 100 that may be used to clean semiconductor process equipment. Bench 100 includes a basket 105 and a pair of baths 110 and 115. Bath 110 contains a quantity of solvent, typically a cleaning solution that includes a strong acid or some other hazardous chemical; bath 110 typically contains de-ionized water. One or more components 120 are cleaned by first immersing basket 105 and components 120 in bath 110 and then immersing basket 105 in bath 115 to rinse the solvent from basket 105 and components 120. Other systems clean and rinse components in the same bath. System 100 can be used for general cleaning, or may be dedicated for use with a particular type of cleaning solution. FIG. 1 also includes a parts holder 130, which typifies another type of parts holder used to support horizontally arranged components 135 during immersion.
Bench 100 is simplified for illustrative purposes. Many cleaning systems include other features, such as additional baths, ultrasonic generators, heaters, coolers, spray nozzles, spargers, and electronic controls. For more information on such cleaning systems, see the brochures entitled xe2x80x9cPA-Series(trademark) Aqueous Precision Cleaning Systems,xe2x80x9d and xe2x80x9cSA-Series(trademark) Solvent Precision Cleaning Systems,xe2x80x9d both by Forward Technology Industries, Inc. (1999). These brochures are incorporated herein by reference.
Conventional cleaning systems have many shortcomings, particularly when used with hazardous liquids to clean components that are very sensitive to contamination. For example:
1. hazardous chemicals can be unintentionally mixed, leading to damaged parts, personal injury, or even death, and immersing components in the wrong liquid can lead to similar problems;
2. the treatment and disposal of hazardous liquids and their vapors is dangerous and expensive;
3. permitting requirements grow more burdensome with increased volumes of hazardous materials; and
4. using large quantities of hazardous materials can be a political liability.
To make matters worse, cleaning different components in the same bath can produce unacceptable levels of cross-contamination. Even removing similar materials from similar parts from different manufacturers can be problematic, as the material being removed from a component from one manufacturer may contain contaminants that are unacceptable to other manufacturers. This source of cross-contamination is increasingly problematic, as decreasing device geometries incite chip manufacturers to explore the use of new materials. It is therefore desirable to minimize the volume of hazardous materials used and created when cleaning components, and further to minimize the possibility of cross-contamination between components from different deposition chambers.
The present invention is directed to cleaning systems and methods that minimize the volume of hazardous materials used and created when cleaning components, and further to minimize the possibility of cross-contamination between components contaminated by different process chemistries.
In accordance with the invention, components to be cleaned are stored within or supported by a dedicated cassette before they are placed in a cleaning receptacle. The cassette is designed to displace a significant percentage of the receptacle""s volume so that only a relatively small volume of cleaning liquid is needed to fully submerge the component. This limits the volume of contaminated cleaning solution. In typical embodiments, the cassette displaces a volume that is greater than the volume of liquid used to clean the component.
In one embodiment in which the cleaning receptacle contains only a single unitary cassette containing a single component of a semiconductor processing system, the cassette displaces a cleaning liquid volume of more than 50% of the total volume of the cleaning receptacle, wherein the cleaning liquid is an acid. The acid is taken from the group consisting essentially of: hydrofluoric acid, nitric acid, hydrochloric acid, and phosphoric acid.
Cassettes may include a handle with an attached pommel adapted to cover the receptacle. The pommel protects a user""s hand from potentially harmful chemicals and, in some embodiments, covers the chemical bath during the cleaning process. Cassettes may also include different configurations of channels that allow cleaning liquid to enter and exit cavities that surround components. The liquid can be moved through the cassette in any number of ways, including by passing bubbles through the channels.
One embodiment of the invention reduces the requisite volume of cleaning solution using a number of liquid-displacing elements (e.g., balls) contained within a cleaning receptacle. Components to be cleaned are then inserted into a bath comprised of cleaning liquid and the displacement elements. The displacement elements raise the level of liquid within the cleaning receptacle, and thereby reduce the amount of cleaning liquid needed to cover the part. The combined liquid and cleaning elements can then be agitated, as with a sparger or ultrasonic wand.
This summary does not purport to define the invention; the claims define the invention.